This invention relates to underdrain filter systems which use sand and gravel as a filtering medium, and more particularly to such a system for use in sewage treatment plants in which the filtration medium is supported above the space provided for the collection of filtered liquid.
Typical underdrain filter systems provide for a downward flow of the liquid through the filtration medium, then through a collection pipe by which it is directed to a selected location. For example, in such an early system described in U.S. Pat. No. 730,518 which issued on June 9, 1903 to F. A. W. Davis, there is shown such a filtering apparatus which includes numerous rectangularly shaped conduits or tiles which have perforations on the top side. These conduits are laid end to end and side by side such that they create a plurality of channels which direct the water or liquid to a collection reservoir. The tops of the conduits or tiles are perforated so that water draining from the filtration medium may enter into the conduits. It will be appreciated, however, that the filtering system described in this patent is unusually susceptible to breakage of the many and numerous tiles. In the event of such breakage, there will not be an even flow of water throughout the entire area of the filter bed. In addition, the tiles are extremely heavy and difficult to put in place by a small crew of workmen. Furthermore, the expense of such complex tiles and the insulation costs make such a system very unattactive when considering cost.
Another U.S. Pat. No. 2,378,239 issued to John P. Myron on June 12, 1945 also uses numerous complex tiles which must be fitted carefully together during installation. Each of these tiles include several chambers some of which are dead end, and others which run the complete length of the tile. The top side of each tile has numerous perforations such that the filtered liquid may flow into the dead ended chambers. Each of the dead ended chambers in turn has holes connecting it to the larger chambers which run the length of the tiles. Thus, although the technique disclosed in the Myron Patent, discloses closely interlocked tiles which are securely attached to the support bed of the filtration system, in a way suitable for allowing backwash during the cleaning of this system and which do provide for an even flow of water through the whole area of the filtered bed, the complex tiles used herein are even more expensive than that discussed in the Davis Patent and require additional effort and skill in the installation thereof.
Still another U.S. Pat. No. 1,770,830 issued to J. G. Barbour, July 15, 1930 illustrates a prior art technique. This patent is somewhat similar to the techniques described heretofore with respect to the Davis and Myron Patents, except that according to this patent there is a first course of channel tiles which are laid on the bed of the filtration system. These channel tiles are then topped with a course of perforated or drain tiles. Thus, the complexity and installation costs are even further increased from the techniques discussed heretofore in that two layers of tiles must be set in place.
Still another U.S. Pat. No. 10,370 issued to M. Stewart on Jan. 3, 1854, illustrating a malt dryer appears to use some of the construction techniques of a filtration system. According to this patent a malt dryer for providing hot air from a furnace includes several horizontal perforated metal sheets. The hot air is forced up through the perforations to dry the malt. The perforated sheets are held in place by the use of supports around the edges of the container and by individual support members at each corner of the perforated sheets. However, it will be appreciated that the purpose of this apparatus is completely different from that of filtration, and other than showing perforated sheets and support blocks is in no way related to the art of filtration or to the present invention.
Other patents describe various types of filtration systems which have some similarities of a sewage filtration system and should be considered in evaluating the technique of the present invention. However, none of these patents show the unusual combination of elements comprising the present invention for fabricating a very inexpensive and simply constructed effective filtration system. For example, U.S. Pat. No. 1,277,832 issued to W. R. Beckley on Sept. 3, 1918 illustrates a filter for corrosive chemicals which uses filtering plates supported at their corners by a corrosive resistance support members. According to this patent, each of the plates constitutes a portion of the filter.
U.S. Pat. Nos. 80,110 issued to T. G. Arnold; 298,172 issued to G. G. Cave; 450,209 issued to W. W. Whiddit; 513,215 issued to H. Strater; 1,686,017 issued to M. B. Lovett; 2,139,924 issued to H. L. Woodruff; 2,127,270 issued to J. Schaff and 4,018,147 issued to O. O. Hensel show various combinations of arrangements of perforated plates used for draining liquids of various types. In addition, U.S. Pat. No. 2,032,668 issued to R. C. Schock on Mar. 3, 1936 includes, in addition to an arrangement of perforated plates, a specific technique for leveling and adjusting the height of these plates. However, as is seen from a review of all of the art discussed above all presently available filtration techniques use either complex tiles or complex perforated plates which are expensive to manufacture and even more expensive to install into the proper locations.
Therefore, to overcome the shortcomings of presently available methods and apparatus, it is an object of this invention to provide methods and apparatus for constructing an inexpensive and simple filtration system.
It is still another object of this invention to provide an effective filtration system that can be readily backwashed.
It is a further object of this invention to provide a filtration system easily transported, and readily installed by a small crew.
To accomplish the above mentioned objects as well as other objects which will become evident from the following drawings and detailed description, the present invention includes an underdrain filtration system comprising a container having a horizontal support base and continuous sides extending above said support base to a selected height. The container support base includes a pipe, trench or other means for carrying the liquid in a selected direction, and toward an aperture located in the side of the container. The container is made of a material such as concrete, tile, stainless steel or the like which is impervious and inert with respect to the liquid being filtered. A multiplicity of adjustable support anchors are rigidly attached to the horizontal support base and extend to the interior of the container. In the case of a concrete container, these support members may, for example, be located in position when the concrete is poured, or may be attached in any other suitable but permanent manner. The support members are also made of a material which is both impervious and inert with respect to the liquid being filtered. A plurality of perforated plates are rigidly attached to the support members such that they form a continuous plane which is parallel to the horizontal support base and at a selected distance therefrom. The perforated plates may have any selected shape and size which is readily handled by a single workman. In addition, the perforated plates are also made of a material which is both inert and impervious to the liquid being filtered. As examples, the plates may be made of fiberglass, PVC, stainless steel, etc. Once the plates are securely in place, a filtration medium such as stones and sand of selected and varying sized are used to fill the space above the perforated plates up to a level necessary to achieve the desired filtration. Thus, it can be seen the liquid to be filtered percolates down through the filtration medium to the perforated plates. The liquid then flows through the perforations of the plates into the space created by the perforated plates and the horizontal support base. From this space, the liquid is routed by the trench in the support base to the aperture in the container sides.